It is known that local area network cables are generally of the type with four twisted pairs of conductors and that the female sockets and the male plugs employed for the connection of such cables include a series of eight metal contacts arranged in a predetermined fashion, most often conforming to the RJ45 format.
It is also known that the geometry of the contacts present in such plugs and in such sockets is not optimal from the electrical transmission point of view and that in particular the disposition of the four pairs of contacts within a single connection unit, with no ground separation, encourages unwanted coupling between the various pairs (known as crosstalk), while the geometry of the contacts is not adapted to the usual characteristic impedance of local area networks, namely 100 ohms, which produces impedance matching faults and therefore high insertion losses.
In order to counterbalance this unwanted coupling and to improve impedance matching, local area network connection devices generally include a compensation circuit between the two connection units formed for example by the contacts of an RJ45 female socket and the terminal block connected to a local area network cable.
This compensation circuit is generally produced in the form of a rigid printed circuit, often including two layers, or even more layers in the case of high-performance sockets.
Such a compensation circuit produces inductive and capacitive coupling, forming an LC cell or a plurality of LC cells in cascade.
The inductive coupling (magnetic coupling or predominantly inductive effect) is produced by the proximity of two wires. The distance that separates them, their dimensions, the materials used for the wires and their supports determine the coupling obtained.
Like inductive coupling, capacitive coupling (electrical coupling or predominantly capacitive effect) is produced by the proximity of two conductors, but it is coupling between the surfaces of these conductors that is required. Capacitive coupling is conventionally produced by comb-shaped capacitors disposed on the same layer of the circuit or through-plated-holes produced through the thickness of the circuit.
One example of a local area network connection device provided with such a compensation circuit is described in French patent application 2 729 510, for example.